Electric power punches for providing a plurality of apertures along one edge of pages to be bound in a looseleaf binder, have been manufactured for many years. They were principally developed to overcome the extremely large forces required to punch a significant number of sheets of paper simultaneously. The punching of typical paper stock in lifts containing more than ten or twelve sheets requires heavy duty mechanical and electrical equipment, while the construction of power punches able to handle lifts of more than twenty sheets are extremely heavy duty and expensive mechanisms.
In view of the large loads required to punch increasingly thick lifts of paper stock, electric punches are typically designed with a lift opening capable of accepting only a thickness which can be successfully punched by the particular machine. From an operator's point of view, such a limited lift opening makes operation of the punch difficult since the rapid insertion of a lift of sheets into the opening is difficult when the opening is the same or only slightly wider than the lift itself. On the other hand, if the lift opening is made substantially larger than the thickness of the maximum punchable lift, the tendency is for the punch operator to insert a larger lift than can be punched by the power system. The result of an excessively thick lift being inserted in the opening is a jam situation wherein the punch does not completely pierce the entire lift and the mechanism is stuck in its jammed condition. While manually operable reversing mechanisms have been employed to reverse the punch after jamming, to our knowledge no prior art system has devised an automatic mechanism by which a jammed machine is prevented.